1. Field of the Invention
The present invention relates to a semiconductor device which has a circuit including a thin film transistor formed using a semiconductor film, and also relates to a manufacturing method thereof. Further, the present invention relates to a display device and a manufacturing method thereof.
2. Description of the Related Art
Display devices are widely spread as displays of televisions and personal computers, cellular phones, and the like, in many of which a liquid crystal display device which uses a thin film transistor including an amorphous silicon (hereinafter, referred to as an amorphous silicon TFT) as a switching element is used. The amorphous silicon TFT is conventionally formed over a glass substrate by a known photolithography process using five photomasks as disclosed in Patent Document 1.
Five photomasks described here include a first photomask for forming a gate electrode, a second photomask for separating a semiconductor layer, a third photomask for forming a source electrode and a drain electrode, a fourth photomask for providing an opening in a protective insulating film, and a fifth photomask for forming a pixel electrode.    [Patent Document 1] Japanese Published Patent Application No. 2001-53283.